1. Field
Embodiments of the present disclosure are directed to a portable ultrasonic flow measuring system.
2. Background
Various measuring methods are known for ascertaining the rate of flow through a tube. The invention relates to the ascertainment of the rate of flow by means of ultrasound. Such measuring systems are also referred to as ultrasonic flow measuring systems. Two methods are prevalent for ascertaining the rate of flow by means of ultrasound: the ultrasonic Doppler method that implements the Doppler Effect and the ultrasonic transit time method that ascertains differences in transit times of transmitted signals and, based on the same, ascertains the velocity of a fluid or medium flowing through a measuring tube. The invention relates to substantially ultrasonic flow measuring systems operating according to the ultrasonic transit time method.
The principle of the ultrasonic transit time method is explained below in greater detail with reference to FIG. 11. For execution of this measuring method, basically at least two ultrasonic transceivers 151, 152 are required, which are used for transmitting and receiving ultrasonic waves. The two ultrasonic transceivers 151 and 152 are attached to a measuring tube 153 such that one transceiver 151 is disposed slightly more downstream than the other. Ultrasonic signals are then transmitted by the first ultrasonic transceiver 151 to the second ultrasonic transceiver 152, and a transit time T1 is measured. Similarly, ultrasonic signals are transmitted by the second ultrasonic transceiver 152 to the first ultrasonic transceiver 151, and again a transit time T2 of the ultrasonic signal is measured. It is necessary for the two ultrasonic transceivers 151 and 152 to be appropriately aligned with each other.
The path of the sound between the two ultrasonic transceivers 151 and 152 is referred to as the signal path 154. An exact alignment of the two ultrasonic transceivers 151 and 152 with each other is important, since otherwise the transmitted signals cannot be received. It might also happen that the signal received is not the direct signal but one reflected by the wall of the measuring tube. This would falsify the measurement.
In FIG. 11, the direction of flow of the fluid flowing through the measuring tube is denoted by an arrow. When ultrasonic signals are now transmitted by the transceiver 151 to the transceiver 152, they move in the direction of flow. The ultrasonic signals transmitted by the transceiver 152 to the transceiver 151 move against the direction of flow. Due to the direction of flow, there is a time difference between the transit time of the ultrasonic waves in the direction of flow T1 and the transit time of the ultrasonic waves against the direction of flow T2. This difference in the transit times is dependent on the velocity of flow. Therefore, the velocity of flow of the medium can be determined by means of the equation
  v  =                    (                              T            2                    -                      T            1                          )                              T          1                ⁢                  T          2                      ·          L              2        ⁢                  cos          ⁡                      (            α            )                              where v is the velocity of flow of the medium, T1 is the transit time of the ultrasonic signal in the direction of flow, T2 is the transit time of the ultrasonic signal against the direction of flow, L is the length of the ultrasonic signal path, and a is the angle of the ultrasonic signal to the direction of flow.
The volumetric rate of flow can be ascertained from the thus determined velocity of flow of the medium in the measuring tube and from the diameter or cross-sectional area of the measuring tube.
Apart from the direct sound path, as denoted by the solid line in FIG. 11, it is also possible to use a signal path reflected on the wall of the measuring tube or a signal path that includes the reflection thereof by the wall of the measuring tube. The reflected signal path is denoted by the dashed line in FIG. 11. In this case, the transceiver 152 would not be used, but rather, a transceiver 152′ would be used in its place. The increased length of the measured distance results in fundamentally more accurate measured values.
However, due to the variables required for computing the velocity of flow such as the angle α and the length L of the ultrasonic signal path, it is important to detect the geometry of the measuring set-up with a high degree of accuracy. Also situations in which the number of reflections is not known should be avoided, since otherwise the length of the ultrasonic signal path would be misjudged.
Basically, two different types of ultrasonic flow measuring systems operating according to the transit time measuring system are known. The first of these consist of permanently installed systems. In these systems, the ultrasonic transceiver is located permanently on or in the measuring tube. This allows the transceivers to be geometrically arranged to a high degree of accuracy. However, the disadvantage of this system is that the sensors must basically remain in or on the tube and thus involve increased capital expenditure. Such systems are mostly used only when substantially continuous monitoring of the flow is required.
By contrast, so-called clamp-on flow meters are known in which ultrasonic sensor heads of an ultrasonic flow measuring system are attached to a measuring tube from outside. This measuring system can be dismantled on completion of the measurement and set up again at another measuring point. However, the disadvantage thereof is that the high requirements of accuracy concerning the geometrical orientation and the transmission of the ultrasonic signals call for a laborious process of installation and adjustment. In addition, the data measured by means of clamp-on devices are far less accurate than data provided by permanently installed systems.
A development of the measuring systems having permanently installed sensors is disclosed in DE 10 2008 033 701 A1. In this case, a special measuring tube is provided, to which an ultrasonic measuring device can be fixed mechanically. The system described in this citation is employed particularly in fields in which continuous measurement is necessary. The advantages of this system are that it is not necessary to remove the complete tube for the purpose of calibrating the measuring system, as is the case in permanently installed measuring sensors, but rather, it is possible to remove only the ultrasonic measuring device. However, in order to ensure that only one specific ultrasonic measuring device can be positioned on a specific measuring tube so as to effect calibration of the tube, additional mechanical identification elements are provided.
However, the ensuing disadvantage is that the ultrasonic measuring device can only be used on this measuring tube, and there is no possibility of flexible use thereof as in the case of clamp-on measuring devices.
US 2008/0236297 A1 describes an ultrasonic measuring device for examining blood vessels. The ultrasonic device comprises a measuring head comprising ultrasonic transceivers that form a measuring path through a central open region of the measuring head, where the blood vessel being examined is fixed in position by means of an inner sleeve attached to an interior surface of the measuring head.
WO 2009/071960 A1 discloses a device for ascertaining the velocity of flow in a tube by means of ultrasound. This is achieved by placing an ultrasonic transmitter on the measuring tube so as to oppose two ultrasonic receivers. Either the transmitter emits wide-angle radiation or it comprises two obliquely disposed transmitters for transmitting ultrasonic waves to the two receivers.
DE 2006 036 720 A1 describes a tube comprising an information carrier that is capable of recording and storing information.